Abstract

Continued population growth is putting increased pressure on Toowoomba's water supply systems. More recently, drought conditions have brought household water use efficiency issues into sharp focus. The Queensland State Government is currently reviewing grey water use under the On Site Sewerage Code of Queensland with a 'Draft for Comment' already circulated. The comments period has closed, and the document is currently with the Queensland Government for finalisation. Toowoomba City Council is actively investigating the potential impacts of this legislative change on the demand for water from the city's storages and on the environmental and health issues that may result from its use.Grey water is the common term for effluent arising from laundry, bath and shower, and kitchen. The quality of grey water can vary considerably depending on its origin within the house.Many people are currently using grey water from their laundries (unlawfully so, as the legislation to make this legal does not come into force until March 2006) to irrigate lawns and gardens. This practice is becoming more popular due to current water restrictions imposed by Council. While seeming to be a harmless activity, long-term use of this water on Toowoomba's soils will result in soil structural degradation, increased soil pH and poor plant growth of those plants adapted to acidic conditions.This suitability study focused on grey water produced by laundries. Laundry grey water contains nutrients such as nitrogen (N) and phosphorus (P). It also contains soluble salts, of which, sodium can have adverse impacts on soil structure. Laundry grey water may also contain bacteria that are harmful to human health.To assess properties of laundry grey water in Toowoomba, samples of laundry water were collected from 15 households in Toowoomba and analysed by the Toowoomba City Council's Laboratory Services for nutrients, salts and faecal coliforms. The volume of water produced by washing machines was also measured, and information collected on the washing machines and detergents used.The water sampled had low salinity levels (if used for irrigation purposes) but very high concentrations of sodium. Phosphorus levels varied with the brand of detergent. Nitrogen concentrations were very low.No faecal coliforms (below the limit of reporting from the laboratory) were recorded for the majority of samples. Only one household produced samples with faecal coliform values that would cause concern. This household contained a baby.The volumes of water used for washing by various households depended on the type of washing machine used. Front loading washing machines used approximately half the water used by top loading machines. The use of front loading machines increased total N and Total Suspended Solid (TSS) concentrations. Front loading machines did not significantly increase the salinity of the water or change the proportion of sodium, calcium, magnesium or potassium cations in the water.A sample from each household type was stored for seven days and the change in nutrients and salts recorded on the second and seventh day of storage. The concentrations of nutrients or salts did not change during storage, but the levels of faecal coliform did increase fifteen-fold in the sample that had a high initial faecal coliform count.Undisturbed core samples of five soils from Toowoomba were collected and leached with two solutions prepared to represent laundry grey water of 'average' and 'poor' quality. The soils were subsequently leached with deionised water to simulate the application of rain water following prolonged irrigation with laundry grey water. The flow rate through the soil samples was recorded during leaching with the saline solutions and with the deionised water. All five soils, when leached with the solution higher in sodium1 (SAR = 23.1), had lower flow rates than when they were leached with the solution lower in sodium (SAR = 9.2).The five soils were also leached with saline solutions and disturbed to simulate what would happen if soils that had been leached with laundry water were disturbed eg a garden bed being dug over or a grassed area subjected to vehicle traffic. All soils leached with high sodicity (SAR = 23.1) and lower salinity2 water (EC = 1.5 dS/m) rapidly dispersed. Soil leached with the lower sodicity water (SAR = 9.2) showed minor soil dispersion or no dispersion at all.